I2G HISTORY OP 



able degree ; and, what is more extraordinary, it is likewise di- 

 lated by cold in the same manner. 



If water be placed over a fire, it grows gradually larger 

 in !>ulk, as it becomes hot, until it begins to boil ; after which 

 no art can either increase its bulk or its heat. By increasing 

 the fire, indeed, it may be more quickly evaporated away ; but 

 its heat and its bulk still continue the same. By the expanding 

 of this fluid, by heat, philosophers have found a way to deter- 

 mine the warmth or the coldness of other bodies ; for if put into 

 a glass tube, by its swelling and rising, it shows the quantity of 

 heat in the body to which it is applied ; and by its contracting 

 and sinking, it shows the absence of the same. Instead of using 

 water in this instrument, which is called a thermometer, they 

 now make use of spirit of wine, which is not apt to freeze, and 

 which is endued even with a greater expansion, by heat, than 

 water.* The instrument consists of nothing more than a hol- 



« Mercury expands by heat and contracts by cold with greater uniformity 

 than even spirit of wine : it is therefore the most proper and the most com. 

 nionly used fur thermometers. There are four different thermometers used 

 at present in Europe ; these are, Fahrenheit's, Celsius's, Reaumur's, and De 

 Lisle's. Fahrenheit's thermometer is used in liritain. The space between tlie 

 boiling and freezing points is divided into ISOo; but the scale begins at the 

 temperature produced by mixing together snow and common salt, which is 

 32' below the freezing point ; of course the freezing point is marked 320, and 

 tlie boiling point 212o. 



The thermometer of Celsius is used in Sweden ; it' has been used also in 

 France since the first revolution, under the name of the thermometre centi- 

 grade. In it the space between the freezing and boiling points, is divided 

 into lOlJO. The freezing point is marked 0, the boiling point lOOo. 



Ihe thermometer known by the name of Reaumur, which was in fact 

 constructed by De Luc, ivas used in France before the revolution, and is still 

 used in Italy and Spain. In it the space between the boiling and freezing 

 points is divided into 80o. The freezing point is marked 0, the boiling 

 point Sf!0. 



De Lisle's thermometer is used in Russia. The space between the boiling 

 and freezing points is divided into 1500; but the gradation begins at the 

 boiling point, and increases towards the freezing point. The boiling point is 

 marked 0, and the freezing point 130o. 



The temperatures which we can measure by a mercurial thermometer are 

 confined within narrow limits. For mercury freezes at about .IQ* below zero, 

 and boils at G60o. Hence we cannot employ it to. measure greater heats than 

 6*J0!>, nor greater degrees of cold than Syo. Yet many temperatures connected 

 •vit!! our most common processes are much Iiigher than GGOu. The heat of a 

 common fire, the temperature at which silver, copper, and gold melts, and 

 many oUier such points, offer familiar examples. — See Dr Thomson's " Out- 

 ine of the Science of Heat and Electiicity," IS30, 8vo. 



